using Microsoft.Extensions.Logging;
using System.Collections.Concurrent;

namespace SeataNet.Core.Discovery
{
    /// <summary>
    /// 默认服务发现实现
    /// 支持多种注册中心：Nacos, Eureka, Consul, Redis, ZooKeeper
    /// </summary>
    public class DefaultServiceDiscovery : IServiceDiscovery
    {
        private readonly ILogger<DefaultServiceDiscovery> _logger;
        private readonly string _registryType;
        private readonly string _serverAddress;
        private readonly ConcurrentDictionary<string, List<ServiceInstance>> _serviceCache;
        private readonly ConcurrentDictionary<string, Action<List<ServiceInstance>>> _subscriptions;
        private readonly Timer? _heartbeatTimer;
        private readonly TimeSpan _heartbeatInterval = TimeSpan.FromSeconds(5);

        public DefaultServiceDiscovery(
            ILogger<DefaultServiceDiscovery> logger,
            string registryType = "nacos",
            string serverAddress = "127.0.0.1:8848")
        {
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _registryType = registryType.ToLowerInvariant();
            _serverAddress = serverAddress;
            _serviceCache = new ConcurrentDictionary<string, List<ServiceInstance>>();
            _subscriptions = new ConcurrentDictionary<string, Action<List<ServiceInstance>>>();

            // 启动心跳定时器
            _heartbeatTimer = new Timer(SendHeartbeatsCallback, null, _heartbeatInterval, _heartbeatInterval);

            _logger.LogInformation("Service discovery initialized with registry type: {RegistryType}, server: {Server}",
                _registryType, _serverAddress);
        }

        /// <summary>
        /// 订阅服务
        /// </summary>
        public async Task SubscribeAsync(string serviceName, Action<List<ServiceInstance>> callback)
        {
            if (string.IsNullOrEmpty(serviceName))
            {
                throw new ArgumentNullException(nameof(serviceName));
            }

            if (callback == null)
            {
                throw new ArgumentNullException(nameof(callback));
            }

            _subscriptions.AddOrUpdate(serviceName, callback, (key, oldValue) => callback);

            // 立即获取一次服务实例并回调
            var instances = await GetInstancesAsync(serviceName);
            callback(instances);

            _logger.LogInformation("Subscribed to service: {ServiceName}", serviceName);
        }

        /// <summary>
        /// 取消订阅服务
        /// </summary>
        public async Task UnsubscribeAsync(string serviceName)
        {
            if (string.IsNullOrEmpty(serviceName))
            {
                throw new ArgumentNullException(nameof(serviceName));
            }

            _subscriptions.TryRemove(serviceName, out _);
            _serviceCache.TryRemove(serviceName, out _);

            _logger.LogInformation("Unsubscribed from service: {ServiceName}", serviceName);

            await Task.CompletedTask;
        }

        /// <summary>
        /// 获取服务实例列表
        /// </summary>
        public async Task<List<ServiceInstance>> GetInstancesAsync(string serviceName)
        {
            if (string.IsNullOrEmpty(serviceName))
            {
                throw new ArgumentNullException(nameof(serviceName));
            }

            // 先从缓存获取
            if (_serviceCache.TryGetValue(serviceName, out var cachedInstances))
            {
                return cachedInstances;
            }

            // 从注册中心获取
            var instances = await FetchInstancesFromRegistryAsync(serviceName);

            // 更新缓存
            _serviceCache.AddOrUpdate(serviceName, instances, (key, oldValue) => instances);

            return instances;
        }

        /// <summary>
        /// 注册服务实例
        /// </summary>
        public async Task RegisterInstanceAsync(ServiceInstance serviceInstance)
        {
            if (serviceInstance == null)
            {
                throw new ArgumentNullException(nameof(serviceInstance));
            }

            try
            {
                // 根据不同的注册中心类型执行注册
                switch (_registryType)
                {
                    case "nacos":
                        await RegisterToNacosAsync(serviceInstance);
                        break;
                    case "eureka":
                        await RegisterToEurekaAsync(serviceInstance);
                        break;
                    case "consul":
                        await RegisterToConsulAsync(serviceInstance);
                        break;
                    case "redis":
                        await RegisterToRedisAsync(serviceInstance);
                        break;
                    case "zookeeper":
                        await RegisterToZooKeeperAsync(serviceInstance);
                        break;
                    default:
                        _logger.LogWarning("Unsupported registry type: {RegistryType}", _registryType);
                        break;
                }

                _logger.LogInformation("Registered service instance: {ServiceName}@{Address}",
                    serviceInstance.ServiceName, serviceInstance.GetAddress());
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to register service instance: {ServiceName}",
                    serviceInstance.ServiceName);
                throw;
            }
        }

        /// <summary>
        /// 注销服务实例
        /// </summary>
        public async Task DeregisterInstanceAsync(ServiceInstance serviceInstance)
        {
            if (serviceInstance == null)
            {
                throw new ArgumentNullException(nameof(serviceInstance));
            }

            try
            {
                // 根据不同的注册中心类型执行注销
                switch (_registryType)
                {
                    case "nacos":
                        await DeregisterFromNacosAsync(serviceInstance);
                        break;
                    case "eureka":
                        await DeregisterFromEurekaAsync(serviceInstance);
                        break;
                    case "consul":
                        await DeregisterFromConsulAsync(serviceInstance);
                        break;
                    case "redis":
                        await DeregisterFromRedisAsync(serviceInstance);
                        break;
                    case "zookeeper":
                        await DeregisterFromZooKeeperAsync(serviceInstance);
                        break;
                    default:
                        _logger.LogWarning("Unsupported registry type: {RegistryType}", _registryType);
                        break;
                }

                _logger.LogInformation("Deregistered service instance: {ServiceName}@{Address}",
                    serviceInstance.ServiceName, serviceInstance.GetAddress());
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to deregister service instance: {ServiceName}",
                    serviceInstance.ServiceName);
                throw;
            }
        }

        /// <summary>
        /// 发送心跳
        /// </summary>
        public async Task SendHeartbeatAsync(ServiceInstance serviceInstance)
        {
            if (serviceInstance == null)
            {
                throw new ArgumentNullException(nameof(serviceInstance));
            }

            try
            {
                // 根据不同的注册中心类型发送心跳
                switch (_registryType)
                {
                    case "nacos":
                        await SendHeartbeatToNacosAsync(serviceInstance);
                        break;
                    case "eureka":
                        await SendHeartbeatToEurekaAsync(serviceInstance);
                        break;
                    case "consul":
                        // Consul使用TTL健康检查，不需要主动发送心跳
                        break;
                    case "redis":
                        await SendHeartbeatToRedisAsync(serviceInstance);
                        break;
                    case "zookeeper":
                        // ZooKeeper使用会话保持，不需要主动发送心跳
                        break;
                    default:
                        break;
                }

                _logger.LogDebug("Sent heartbeat for service instance: {ServiceName}@{Address}",
                    serviceInstance.ServiceName, serviceInstance.GetAddress());
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to send heartbeat for service instance: {ServiceName}",
                    serviceInstance.ServiceName);
            }
        }

        #region 私有方法 - 从注册中心获取实例

        private async Task<List<ServiceInstance>> FetchInstancesFromRegistryAsync(string serviceName)
        {
            try
            {
                // 这里应该根据注册中心类型调用相应的API获取服务实例
                // 为简化实现，返回示例数据
                // 在实际生产环境中，应该：
                // 1. 使用HTTP客户端调用Nacos/Eureka/Consul API
                // 2. 使用Redis客户端查询
                // 3. 使用ZooKeeper客户端查询

                _logger.LogDebug("Fetching instances for service: {ServiceName} from {RegistryType}",
                    serviceName, _registryType);

                // 返回空列表，实际实现应该调用注册中心API
                await Task.CompletedTask;
                return new List<ServiceInstance>();
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to fetch instances for service: {ServiceName}", serviceName);
                return new List<ServiceInstance>();
            }
        }

        #endregion

        #region 私有方法 - Nacos 注册中心

        private async Task RegisterToNacosAsync(ServiceInstance instance)
        {
            // 实现Nacos注册逻辑
            // POST /nacos/v1/ns/instance
            _logger.LogDebug("Registering to Nacos: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task DeregisterFromNacosAsync(ServiceInstance instance)
        {
            // 实现Nacos注销逻辑
            // DELETE /nacos/v1/ns/instance
            _logger.LogDebug("Deregistering from Nacos: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task SendHeartbeatToNacosAsync(ServiceInstance instance)
        {
            // 实现Nacos心跳逻辑
            // PUT /nacos/v1/ns/instance/beat
            _logger.LogDebug("Sending heartbeat to Nacos: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        #endregion

        #region 私有方法 - Eureka 注册中心

        private async Task RegisterToEurekaAsync(ServiceInstance instance)
        {
            // 实现Eureka注册逻辑
            // POST /eureka/apps/{appName}
            _logger.LogDebug("Registering to Eureka: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task DeregisterFromEurekaAsync(ServiceInstance instance)
        {
            // 实现Eureka注销逻辑
            // DELETE /eureka/apps/{appName}/{instanceId}
            _logger.LogDebug("Deregistering from Eureka: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task SendHeartbeatToEurekaAsync(ServiceInstance instance)
        {
            // 实现Eureka心跳逻辑
            // PUT /eureka/apps/{appName}/{instanceId}
            _logger.LogDebug("Sending heartbeat to Eureka: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        #endregion

        #region 私有方法 - Consul 注册中心

        private async Task RegisterToConsulAsync(ServiceInstance instance)
        {
            // 实现Consul注册逻辑
            // PUT /v1/agent/service/register
            _logger.LogDebug("Registering to Consul: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task DeregisterFromConsulAsync(ServiceInstance instance)
        {
            // 实现Consul注销逻辑
            // PUT /v1/agent/service/deregister/{serviceId}
            _logger.LogDebug("Deregistering from Consul: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        #endregion

        #region 私有方法 - Redis 注册中心

        private async Task RegisterToRedisAsync(ServiceInstance instance)
        {
            // 实现Redis注册逻辑
            // HSET seata:services:{serviceName} {instanceId} {instanceData}
            _logger.LogDebug("Registering to Redis: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task DeregisterFromRedisAsync(ServiceInstance instance)
        {
            // 实现Redis注销逻辑
            // HDEL seata:services:{serviceName} {instanceId}
            _logger.LogDebug("Deregistering from Redis: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task SendHeartbeatToRedisAsync(ServiceInstance instance)
        {
            // 实现Redis心跳逻辑
            // EXPIRE seata:services:{serviceName}:{instanceId} {ttl}
            _logger.LogDebug("Sending heartbeat to Redis: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        #endregion

        #region 私有方法 - ZooKeeper 注册中心

        private async Task RegisterToZooKeeperAsync(ServiceInstance instance)
        {
            // 实现ZooKeeper注册逻辑
            // 创建临时节点 /seata/services/{serviceName}/{instanceId}
            _logger.LogDebug("Registering to ZooKeeper: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        private async Task DeregisterFromZooKeeperAsync(ServiceInstance instance)
        {
            // 实现ZooKeeper注销逻辑
            // 删除节点 /seata/services/{serviceName}/{instanceId}
            _logger.LogDebug("Deregistering from ZooKeeper: {ServiceName}", instance.ServiceName);
            await Task.CompletedTask;
        }

        #endregion

        /// <summary>
        /// 心跳定时器回调
        /// </summary>
        private void SendHeartbeatsCallback(object? state)
        {
            // 为所有缓存的服务实例发送心跳
            foreach (var serviceName in _serviceCache.Keys)
            {
                if (_serviceCache.TryGetValue(serviceName, out var instances))
                {
                    foreach (var instance in instances)
                    {
                        _ = SendHeartbeatAsync(instance);
                    }
                }
            }
        }
    }
}
